In recent years, a technology for ensuring the security of a server system has become more important to prevent leakage of information, such as personal information and confidential information of enterprises, to outsiders. As such a technology, there has been proposed, as disclosed in Patent Literature 1, for example, a method of, when input data contains information that should be protected, providing a mark, which indicates that the information is the target to be protected, to the input data, and propagating the same mark for data that is newly generated as a result of processing the input data. Accordingly, it is possible to block output of the original data as well as the newly generated data to the outside.